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SHI Yuxin,XIE Lingling,ZHENG Quanan,ZHANG Shuwen,LI Mingming,LI Junyi. 2019. Unusual coastal ocean cooling in the northern South China Sea by a katabatic cold jet associated with Typhoon Mujigea (2015). Acta Oceanologica Sinica, 38(5):62－75

Unusual coastal ocean cooling in the northern South China Sea by a katabatic cold jet associated with Typhoon Mujigea (2015)

2015年台风“彩虹”过境后下山冷急流引起的南海北部海域异常海面降温

Received:March 16, 2018

DOI：10.1007/s13131-019-1440-4

Key words:Typhoon Mujigea (2015) second-round cooling katabatic cold jet South China Sea westerly wind front

中文关键词: 台风“彩虹” 二次降温下山冷急流南海西风带

基金项目:Foundation item:The National Natural Science Foundation of China under contract Nos 41776034, 41476009 and 41706025; the GASI Project under contract Nos GASI-IPOVAI-01-02 and GASI-02-SCS-YGST2-02; the Natural Key Research and Development Program of China under contract No 2016YFC1401403; the Foundation of Guangdong Province for Outstanding Young Teachers in University under contract No. YQ201588.

Author Name	Affiliation	E-mail
SHI Yuxin	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
XIE Lingling	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China	llingxie@163.com
ZHENG Quanan	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland 20742, USA
ZHANG Shuwen	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
LI Mingming	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
LI Junyi	Guangdong Key Laboratory of Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China

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Abstract:

This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea (SCS) in October 2015. We analyze the satellite sea surface temperature (SST) time series from October 3 to 18, 2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of -2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7 d of the typhoon passage, and lasted for 5 d from October 10 to 15. The maximum SST cooling was -4℃ and occurred after 12 d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau (YGP), Typhoon Mujigea (2015) met the westerly wind front on October 5. The low-pressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough, thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau (QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4 d later after the maximum air temperature drop of -9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.

中文摘要:

本文研究了2015年10月台风"彩虹"过境南海北部陆架后，近岸海域发生的异常降温事件。通过分析10月3日-18日海面温度SST卫星资料的时间序列，发现近岸降温过程分为两个不同的阶段。第一阶段降温，自10月3日台风过境后立即发生，至10月7日达到最大降幅-2℃，这与台风过境后常见的冷迹现象类似。第二阶段为异常降温，自10月10日即台风过后7天开始，持续降温5天，于10月10月15日达到最大降幅-4℃，此时已是台风过境后第12天。天气图分析发现，台风"彩虹"登陆后继续西北方向前行，于10月5日到达云贵高原一带，与北侧的西风带锋面相遇。台风的低压及正涡度扰动增强了锋面不稳定，诱发了经向大气流动，从而使得青藏高原的冷空气以下山冷急流风（katabatic jet）形式南下，途径云贵通道，入侵南海北部。二次降温过程中，气温于10月11日达到最大降温，降幅-9℃，海洋最大降温时间比大气晚4天。近岸三个区域的同步气温和海温的对比分析表明，正是台风扰动引起的下山冷急流的入侵，使得南海北部海域SST在台风过境后出现了异常的二次降温现象。

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